In a molten-glass-producing apparatus, hollow tubes made of platinum or a platinum alloy such as platinum-gold or platinum-rhodium for conduit tubes for molten glass such as an uprising pipe or a downfalling pipe of a vacuum degassing apparatus (refer to Patent Document 1). The reason why such hollow tubes made of platinum or a platinum alloy are used for conduit tubes for letting molten glass having a temperature of from 1,100 to 1,500° C. flow through, is not only because these metals have high melting points but also because these materials have low reactivity with molten glass even at high temperature, whereby no inhomogeneity of molten glass due to their reaction with the materials is produced, and their strength at high temperature can be maintained to a certain extent. However, since platinum and platinum alloys are expensive materials, the thickness of the hollow tube is preferably as thin as possible. As a material having both the above-mentioned excellent property of platinum or platinum alloys and mechanical strength, a reinforced platinum produced by dispersing metal oxide particles such as Al2O3, ZrO2 or Y2O3 into platinum or a platinum alloy, is starting to be used as a material constituting the hollow tube. In such a reinforced platinum, metal oxide particles dispersed in platinum or a platinum alloy produce an effect of preventing dislocation or movement of grain boundaries, to increase mechanical strength.
Patent Document 1: Japanese Patent No. 2817168